This invention relates generally to furnaces for semiconductor wafer processing and, more particularly, to a process tube support sleeve used in high temperature processing.
For a number of reasons, furnaces commonly used for semiconductor processing have shortcomings.
For example, furnaces used in the semiconductor industry for high temperature processing, e.g., processing at temperatures in the range of about 1100xc2x0 C. to 1350xc2x0 C., typicallly use process tubes formed of SiC (silicon carbide). Silicon carbide is used to form the process tubes because it desirably is a material that can withstand high temperatures and because it is available in adequate purity for use in semiconductor processing.
A problem encountered with SiC, however, is that it has a high thermal conductivity. Because of this high thermal conductivity, the extremities of a SiC process tube, located away from the heating elements in a furnace, remain very hot even in comparison to parts of the process tube next to those heating elements. Thus, SiC can conduct heat away from the areas near the heating elements, resulting in undesirable heat loss at the extremities of the process tube. To minimize heat loss away from the process tube, U.S. Pat. No. 5,662,470, assigned to ASM International N.V., describes use of a quartz support sleeve, which is less thermally conductive than a similar part made of SiC, between the process tube and a cooler metal support structure.
Where various parts of a furnace meet, a seal is generally required to prevent leakage of process gas out to the ambient environment and leakage of ambient air into the process tube. Because of its high thermal conductivity, the temperature of a SiC process tube at the location of a seal will be close to the operating temperature of the furnace and, so, the seal should be temperature resistant, especially if the furnace: is used for high temperature processing. In U.S. Pat. No. 5,662,470 a seal is formed by simply contacting surfaces of the SiC process tube with surfaces of the quartz support sleeve. Such a seal, however, can still allow some leakage of process gas and ambient air and so, is not adequate for use in cases where a high purity atmosphere inside a process tube is required.
In addition to problems stemming from process tube atmosphere purity requirements, another problem relating to furnaces stems from thermal effects caused by feeding gases into a vertical furnace. Before entering the furnace, a gas should be heated from room temperature to the process temperature. In one design according to the prior art, a gas feed tube is mounted on the outside of the process tube. Gas is supplied, at the bottom of the feed tube, located near the bottom of the process tube, and flowed in an upward direction through the feed tube to the top of the furnace, where it is introduced centrally into the reaction chamber. This scheme causes radial asymmetries in temperature over the length of the process tube because the gas, while flowing through the gas feed tube and up the length of the process tube, heats up by withdrawing heat from the furnace where the gas feed tube is located. In addition, gas introduction at the process tube top results in stronger thermal effects on the uppermost wafers relative to the lower wafers.
Apart from thermal effects caused by a gas feed, the movement of gas feeding into and exhausting out of a process tube can give rise to a flow pattern inside the process tube that is not cylindrically symmetrical, i.e., the flow pattern is not symmetrical over horizontal cross-sections of the process tube. This asymmetrical flow pattern can give rise to non-uniformities in the process results on wafers processed in the process tube.
One possible solution for minimizing these non-uniformities in process results is to rotate, during processing, the boat containing the wafers. By rotating the wafers, local non-uniformities are smeared or averaged out over a complete circle. However, for high temperature applications it is difficult to provide a boat rotation mechanism and rotation feed-through that is sufficiently resistant to the high temperatures (e.g., 1100xc2x0 C.-1350xc2x0 C.) employed in such applications.
A further problem with commonly used furnaces is that manufacturing a SiC process tube is costly and complicated, especially when gas feed tubes or gas distribution tubes need to be incorporated into the process tube.
Accordingly, it is an objective of the present invention to provide methods and structures for a furnace that overcome one or more of the disadvantages and difficulties discussed above.
In accordance with one preferred embodiment of the invention, a support sleeve is provided for supporting a process vessel in a furnace for semiconductor processing. The sleeve comprises a top and a bottom surface and a wall defining the support sleeve. The wall has at least one channel, with surfaces of the wall defining sides of the channel. The channel extends in a horizontal direction along the wall and is connected to a gas communication line.
In accordance with another preferred embodiment, a semiconductor processing furnace is provided. The furnace comprises a process vessel support sleeve having a first surface on which the process vessel is supported, the first surface having a perimeter. The furnace also comprises a process vessel that overlies the support sleeve and has a second surface. The second surface contacts the first surface, which has an opening in that surface. The opening extends along a length of the interface between the first surface and the second surface and the interface extends along the length of the perimeter of the support sleeve.
In accordance with yet another preferred embodiment, a method is provided for forming a seal between parts of a semiconductor processing furnace. The method comprises circulating a gas inside a first sealing channel that is defined by surfaces of a wall. The first sealing channel is open to a first contact surface with a first contact part. The wall defines a support sleeve and partially separates a reaction space for processing wafers and an ambient atmosphere. The support sleeve supports a process tube. The method further comprises generating a first pressure differential, where a first sealing channel gas pressure is either greater than both a reaction space gas pressure and an ambient atmosphere gas pressure or the sealing channel gas pressure is less than both the reaction space gas pressure and the ambient atmosphere gas pressure.
In accordance with yet another preferred embodiment, a method is provided for manufacturing semiconductor devices. The method comprises flowing a gas around an interior of a wall defining a support sleeve that supports a process, around the sleeve""s circumference, and expelling the gas out of a surface of the support sleeve.